Digitally controlled attenuators are known. Typically, such attenuators comprise a resistive divider network coupled to a multiplexer, which may be controlled to route an attenuated version of an input signal to an output port. The problem with conventional attenuators, however, is that they often provide non-monotonic attenuation, particularly when large numbers of small attenuation steps are required. That is, when the attenuator is controlled to select the next highest attenuated signal, the actual output signal actually increases (i.e., lower attenuation) in amplitude (and vice versa).
To solve this problem, some attenuator designers have employed high precision parts (for example, resistors having a 1% or better tolerance). However, this practice greatly increases the cost of the attenuator without fully solving the non-monotonic operation of the attenuator.
Accordingly it is an object of the present invention to provide a monotonic digitally controlled attenuator having a large number of attenuation steps.
It is a further object of the present invention to provide a monotonic digitally controlled attenuator that may be implemented with low precision (i.e., resistors having a 5% tolerance) components.